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The unprecedented magnitude of the Deepwater Horizon oil spill presents significant challenges for oil spill responders and those tasked with assessing the impacts of the spill. Evaluating changes to ecosystem services—the benefits people receive from natural resources and processes—caused by the oil spill could expand the potential to capture and value the full breadth of impacts to the ecosystem and the public. This report assesses the methods and metrics that could help scientists effectively evaluate ecosystem services.

Key Messages

The Oil Pollution Act of 1990 establishes a formal legal framework for determining when an oil spill results in an "injury"-- defined as an observable or measurable adverse change or impairment in a natural resource. This requires assessment of the extent and severity of an injury to a natural resource through a process known as the Natural Resources Damage Assessment (NRDA). In addition to quantifying the extent of damage the assessment includes plans for developing, implementing, and monitoring restoration and compiles expenses for both assessment and restoration costs from those deemed responsible.

The magnitude and depth of the Deepwater Horizon oil spill, together with the inherent complexity of the Gulf of Mexico ecosystem, pose serious challenges to those charged with assessing damages and developing restoration plans. For a spill the size of the Deepwater Horizon, an "ecosystem services approach" may complement the Natural Resources Damage Assessment and offer a broader opportunity to capture, value, and appropriately restore the full breadth of impacts to the ecosystem and the public. This approach would focuses not only on replacing or repairing damaged natural resources but also on re-establishing or replacing the ecosystem's interdependent processes.

In order to assess the impacts of the Deepwater Horizon oil spill, scientists need to establish a baseline of ecosystem conditions before the spill took place. However, there are natural variations in conditions in the Gulf of Mexico over time, as well as human-made changes to the environment. Analysis of the impact of the Deepwater Horizon oil spill will need to take into account the fundamental complexity of the Gulf of Mexico ecosystem, and the past and ongoing affects of phenomena, both natural and human-induced, that are unrelated to the Deepwater Horizon oil spill.

Implementing an ecosystem approach to damage assessment requires an understanding of the complex linkages amongst various ecosystem components, including the impact of humans on the structure and function of the ecosystem, the resulting changes in ecosystem services, and how these changes affect human well-being.

Determining the impact of human actions on the structure and function of the ecosystem
Scientists will need to investigate each ecosystem service by carrying out specific types of sampling and analysis to complement the information collected under the existing damage assessment process. In order to extend the current damage assessment to include an ecosystem services approach, scientists need to understand how these various components have been affected by human actions, the consequences for the structure and function of the ecosystem, and ultimately the changes in ecosystem services caused by the spill.

Establishing how changes in the ecosystem lead to changes in ecosystem services
This step determines ecosystem production functions –how the ecosystem transforms inputs into outputs such as the yields of crops or fisheries. For many ecosystem services, a lack of mechanistic understanding and data inhibits accurate quantification of ecosystem services. The complexity of marine ecosystems makes it difficult to understand how disturbances to an ecosystem will reverberate through the system and ultimately lead to changes in the provision of ecosystem services.

Establishing how changes in the provision of ecosystem services affect human well-being.
The third component of the ecosystem services approach focuses on establishing the value of ecosystem services. This involves combining economic methods with ecological assessments to estimate the value of changes in ecosystem services as a result of environmental impacts. Valuation methods are used to provide a common, quantitative measure to facilitate comparisons among various services as an indication of how much the availability of the service contributes to the improvement in human well-being. Alternatively, in the case of damage to the environment, valuation methods could be applied to assess how much value has been lost as a consequence of reduced ecosystem services.